In the previous paper by authors, fatigue limit and the stress at the transition point, the point where the deformation mechanism of the material changed from visco elastic into visco elastic-plastic behavior, of mild steel were found to be almost identical under constant-amplitude loading conditions, and the visco elastic-plastic constitutive equation which represent cyclic stress-strain response of mild steel was derived. In this paper, complete compression-to-tension load-controlled axial loading test programs-constant amplitude and random loading with an exponential distribution of stress amplitude- were performed for mild steel plane specimens. From the test results, coefficients in the visco elastic-plastic constitutive equation derived in the previous paper are given as a function of both the value of applied stress and their cycles. Then, the correlation between fatigue limit and the stress at the transition point is discussed. As a result, following four main points are obtained. 1) There is a good correlation between fatigue limit and the stress at the transition point under variable-amplitude loading conditions. 2) The transition point stress decreases when stresses larger than fatigue limit (corresponding to the transition point stress) are applied, and then converges to a certain value, depending on the value of the larger applied stresses and their cycles. 3) Given the condition of variable amplitude loading, the transition point stress can be calculated using the derived constitutive equation. 4) Using the above results, a method for determining fatigue limit under variable-amplitude loading conditions is proposed.